Vehicle systems may include multiple coolant loops for circulating coolant through distinct sets of engine components. The coolant flow may absorb heat from some components (thereby expediting cooling of those components) and transfer the heat to other components (thereby expediting heating of those components). For example, a high temperature coolant loop may circulate coolant through an engine to absorb waste engine heat. The coolant may also receive heat rejected from one or more of an EGR cooler, an exhaust manifold cooler, a turbocharger cooler, and a transmission oil cooler. Heat from the heated coolant may be transferred to a heater core (for heating a vehicle cabin), and/or dissipated to the atmosphere upon passage through a radiator including a fan. As another example, a low temperature coolant loop may circulate coolant through a charge air cooler. When required (such as when cabin air conditioning is requested), coolant in the low temperature loop may be additionally pumped through the condenser of an air conditioning (AC) system to absorb heat rejected at the condenser by a refrigerant of the AC system. Heat from the heated coolant may be dissipated to the atmosphere upon passage through another radiator including a fan. One example of such a vehicle coolant system is shown by Ulrey et al. in US20150047374. Another example coolant system is shown by Isermeyer et al. in US20150040874. Therein a heat exchanger enables heat exchange between a charge air cooling coolant circuit and a refrigerant circuit of the condenser.
The inventors herein have recognized that by coordinating the actuation of an electric coolant pump and a proportioning valve, flow may be better apportioned between the different components of a coolant circuit requiring coolant flow (such as an AC condenser and a charge air cooler), allowing for improved cooling with reduced parasitic losses. In particular, for a given cooling demand, there may be a specific combination of coolant pump output and coolant flow rate through the AC system relative to coolant flow through a CAC that reduces parasitic losses. At this operating point, the engine may be operated to meet all cooling demands with higher fuel economy. By mapping the relation between coolant flow rate, pump output, and AC head pressure, an operating point where both coolant pump efficiency is high and AC condenser efficiency is high can be identified and provided at higher fuel economy.
In one example, this may be achieved by a method comprising: estimating a requested coolant flow rate through a coolant circuit based on a cooling demand at each of an air-conditioning condenser, a charge air cooler (CAC) and a transmission oil cooler (TOC) of the coolant circuit; estimating an effective flow resistance through the coolant circuit based on a position of a first valve coupled to the condenser and the CAC, and a second valve coupled to the TOC; and adjusting a coolant pump output based on the estimated flow resistance to provide the requested coolant flow rate. In this way, coolant flow may be better proportioned between components of the coolant circuit based on demand and performance, while improving fuel economy.
As an example, each of a condenser of an AC system and a CAC may be coupled to distinct branches of a coolant circuit downstream of a proportioning valve, coolant directed into the circuit via a coolant pump. The condenser may be further coupled to a refrigerant circuit of the AC system, while the coolant circuit may be further coupled to an oil circuit of a transmission at a transmission oil cooler (TOC). The AC condenser may be positioned towards a rear end of the under-hood area. During vehicle operation, as driver demand and cabin cooling demand changes, the apportioning of coolant flow to each branch may be varied. For example, when cabin cooling is demanded, a desired coolant temperature is determined. Then, by referring a 2D map or model that maps a relationship between the coolant flow rate, the desired coolant temperature, and an AC head pressure, taking into account parasitic losses, a target coolant flow rate through the AC condenser may be determined (as the point of minima of the asymptote of the 2D map). In particular, there may be a coolant flow rate above which the change in coolant temperature is not significant due to an increase in parasitic losses at the CAC. This coolant flow rate may be set as the desired coolant flow rate through the AC loop. In addition, a corresponding reference AC head pressure may be determined. The coolant flow rate may be determined while taking into account the flow resistance through the different coolant circuit components due to the position of corresponding valves. For example, as a valve coupled to the TOC is opened, to enable coolant flow through the TOC to reduce the chance of transmission oil boiling over, the effective flow resistance of the circuit is decreased. As another example, based on the position of the proportioning valve, a flow resistance through the condenser and the CAC may vary. The controller may determine a pump output that provides the target coolant flow rate at the given position of the valves. Then, based on a relative priority status of the different components (which is a function of their relative cooling demand), the controller may further update the proportioning valve position. For example, the proportioning valve position may be adjusted so that the component with higher priority has its coolant flow demand met while the remaining component with lower priority receives excess flow. Further, during conditions when no cabin cooling is demanded, a minimum coolant flow rate may be provided through the condenser. During conditions when both cabin cooling demand and engine cooling demand is saturated, a fixed, calibrated coolant flow rate may be provided through both the AC condenser and the CAC.
In this way, coolant flow may be apportioned to different components to meet their cooling demands in a fuel efficient manner. By relying on an inverse model to determine a coolant pump and proportioning valve setting that enables a coolant flow rate while accounting for flow resistances through the different flow paths of the coolant circuit, open loop control of the coolant circuit may be simplified. In particular, the modeling may be performed with a simpler model without compromising accuracy. Further, the model provides a central place where settings can be changed to accommodate different hydraulic arrangements. By accounting for branch resistance and viscosity, branch flow requests can be met while also meeting a minimum parallel branch flow. As such, this reduces parasitic losses while still meeting the required cooling. Overall, engine cooling performance is improved.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.